The ras oncogene, which is responsible for tumorigenesis, has been cloned into an E. coli expression vector, and its gene product can be obtained in a large amount which is sufficient for biochemical and enzymological analyses. Using this protein, we will be able to characterize the biochemical activity of ras oncogene products in growth control and receptor-mediated signal transfer. We will also make monoclonal antibodies against the synthetic peptides, which are expected to be able to detect the mutations in ras genes. These antibodies will be a powerful tool for diagnosis of cancer at the biochemical level.